Combined addition agents for acid copper plating



Richard E. Woehrle,

COIVIBINED ADDITION AGENTS FOR ACID COPPER PLATING Tralford, and James W. Condon,

Westinghouse Electric Cor- Pittsburgh, Pa., assignors to a corporation of Pennporation, East Pittsburgh, Pa., sylvania No Drawing. Application February 26, 1954, Serial No. 412,948

8 Claims. (Cl. 204-52) Thisinvention relates-to the electrodeposition of copper from acid electrolytes embodying a combination of certain addition agents to promote brighter and smoother electrodeposits.

It is a general practice in the use of standard acid copper plating solutions to add a brightening agent to promote brighter and smoother deposits. An excellent brightening agent which has been recently developed is 2-thiohydantoin or certain substitution derivatives of 2- thiohydantoin. Under operating conditions, however, a disadvantage found with the use of 2-thiohydantoin compounds as a brightening agent was thatof short life, such that they have to be replaced in the electrolyte at the end of from 2 to 3 hours of plating. This results not only in more work for the plater, but also increases the plating costs since the Z-thiohydantoin compound is expensive to replace.

An object of thisinvention is to provide an acid copper electrolyte containing a long lasting novel combination of addition agents comprising dextrose and 2-thiohydantoin or certain substitution derivatives of Z-thiohydantoin.

A further object of this invention is to provide an acid copper electrolyte containing a long lasting novel combination of addition agents comprising dextrose, 2-thiohydantoin or certain substitution derivatives of 2-thiohydantoin, and a metal dialkyl dithiocarbamate.

A still further object of this invention is to provide a process for electroplating copper from an acid copper electrolyte containing dextrose and 2-thiohydantoin or certain substitution derivatives of Z-thiohydantoin, either with or without the addition of a metal dialkyl dithi'o'carbamate.

Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter.

For a better understanding of the nature of the objects of the invention, reference should be had to the following detailed description.

We have discovered that the addition of certain proportions of dextrose with a 2fthiohyd'antoin compound to acid copper" electrolytes will enable electrodeposit'ion over long periods of time of copper having a highly refined grain size and smooth, bright surfaces from the electrolyte so treated. The addition of dextrose unexpectedly prolongs the life of 2-thiohydantoin to from 4 to 5 times of what it would be without the dextrose. The specificity of the dextrose is evident from the fact that additions of dextrin in any amount have no comparable beneficial eifect on the life of the Z-thiohydantoin additions, the improvement in life being 30 to 40% when using dextrin. The present invention is based on the addition to the acid copper electrolyte of from 0.01 to 1.0 ounce per gallon of dextrose and from 0.0005 to 0.05 ounce per gallon of at least one Z-thiohydantoin or certain substitution derivatives of 2-thiohydantoin.

Patented July 16, 1957 The thiohydantoin compounds used in this invention are those having the following base structure:

The 1, 3 and 5 positions may be filled by hydrogen atoms or at least one organic radical may be substituted at any one or more of the 1, 3, or 5 positions, so long as the compound is not rendered so insoluble that it will not dissolve in the acid copper electrolyte in an amount suflicient to produce an appreciable result. Ex amples of suitable compounds are: Z-thiohydantoin l-acetyl-Z-thiohydantoin 5 (Z-hydroxylbenzal) -2-thiohyd antoin 5-furfural-Z-thiohydantoin 1E-benzoyl-2-thiohydantoin S-ben-zal-Zthiohydantoin l-methyl-Z-thiohydantoin 3-acetyl-2-thiohydanfoin- The best results have been securedwith thiohyd'antoin compounds having acarbonyl group attached at any one or all of the 1', 3, and 5 positions, and with an organic radical being attached to the carbonyl group.

Furthermore, we have discovered that even brighter copper deposits are obtained if from 0.001 to 0.1 ounce per gallon of a metal dialkyl dithiocarbamate compound is added to the above formulation of this invention. The addition to the electrolyte of a metal dialkyl dithioca'p bamate compound however, is optional: depending upon the brightness desired in the final product.

The metal dialkyl dithiocarbamate compounds used in this invention have the nucleus where M is a metal selected from the group consisting of cadmium, cobalt, nickel, and zinc, and R1, R2, R3, and Ri are the same or different alkyl homol o'g's selected from at least one of the groupconsistin'g of monova'lent hydrocarbon radicals' containing from 1 to 6 carbon atoms; Various organic'radica'ls may besubstituted for any one of the R1, R2;.Ra', and R4=h0rnolOgs so longiasthe'resulting compound is not rendered so insoluble that it will not dissolve in the copper plating electrolyte in an amount An aqueous electroplating electrolyte of the following composition was prepared:

Ozs. per gallon Copper sulfate (crystals) [CuSO4.6H2O] 27.5 Sulfuric acid (98%) 6 Dextrose 0.5

This bath was operated at a temperature of 90 F. Copper was plated on a cathode base immersed in the bath using direct current at current densities of from 10 to 100 amperes per square foot at the cathode. In each case the copper had a highly refined grain and was quite bright.

A cathode was placed in the bath and plated using a periodic reverse current cycle of 20 seconds plating and seconds deplating at 50 a. s. f. during both periods. Bright, smooth copper was plated therewith.

l-acetyl-Z-thiohydantoin Example II An aqueous electroplating electrolyte was prepared and operated in the same manner as Example I except that 0.01 ounce per gallon of zinc dibutyldithiocarbamate was added to the bath formulation. A substantially brighter deposit was produced with the bath of Example II.

The electrolytes of both Examples I and H had a prolonged plating life of approximately hours. Without the addition of dextrose, the maximum life that could be expected would be 3 hours.

The addition agents of this invention may be formulated and added to an acid copper electrolyte when desired. The formulation comprises from 5 to 30 parts by weight of at least one thiohydantoin compound and from 70 to 95 parts by weight dextrose. If a substantially brighter deposit is to be plated, from 5 to parts by weight of a metal dialkyl dithiocarbamate compound are admixed with each 100 parts by weight of the above thiohydantoindextrose formulation.

Since certain changes may be made in the above invention and different embodiments of the invention may be made without departing from the scope hereof, it is intended that all matter contained in the disclosure shall be interpreted as illustrative and not in a limiting sense.

We claim as our invention:

1. An aqueous electroplating electrolyte comprising essentially copper sulfate, sulfuric acid, from 0.01 to 1.0 ounce per gallonof dextrose and from 0.005 to 0.015 ounce per gallon of 1-acety1-2-thiohydantoin.

2. The aqueous electroplating electrolyte of claim 1 in which there is present from 0.001 to 0.1 ounce per gallon of Zinc dibutyldithiocarbamate.

3. In the process of plating on a base copper from an aqueous electrolyte, the electrolyte comprising essentially copper sulfate and sulfuric acid, the steps comprising adding from 0.01 to 1.0 ounce per gallon of dextrose and from 0.0005 to 0.015 ounce per gallon of l-acetyl-Z-thiohydantoin to the electrolyte and passing an electrical current therethrough from an anode to the base to deposit copper on the base.

4. In the process of plating on a base copper from an aqueous electrolyte, the electrolyte comprising essentially copper sulfate and sulphuric acid, the steps comprising adding from 0.01 to 1.0 ounce per gallon of dextrose, from 0.0005 to 0.015 ounce per gallon of l-acetyl-Z-thiohydantoin, and from 0.001 to 0.1 ounce per gallon of zinc dibutyldithiocarbamate to the electrolyte and passing an electrical current therethrough from an anode to the base to deposit copper on the base.

5. An aqueous electroplating electrolyte comprising essentially copper sulfate, sulfuric acid, from 0.01 to 1.0 ounce per gallon of dextrose and from 0.0005 to 0.015 ounce per gallon of at least one Z-thiohydantoin compound.

6. The aqueous electroplating electrolyte of claim 5 in which there is present from 0.001 to 0.1 ounce per gallon of an addition agent having the nucleus where M is a metal selected from the group consisting of cadmium, cobalt, nickel, and zinc and R1, R2, R3, and R4 are selected from at least one of the group consisting of monovalent hydrocarbon radicals containing from 1 to 6 carbon atoms.

7. A combination of addition agents for use in aqueous acid copper electrolytes comprising as its essential ingredients from 5 to 30 parts by weight of at least one 2-thiohydantoin compound and to parts by weight of dextrose.

8. The combination of claim 7 in which there is present for each parts of the above formulation from 5 to 15 parts by Weight of an addition agent having the nucleus References Cited in the file of this patent UNITED STATES PATENTS Phillips et al Aug. 7, 1951 Jernstedt et a1. Jan. 18, 1955 

1. AN AQUEOUS ELECTROPLATING ELECTROLYTE COMPRISING ESSENTIALLY COPPER SULFATE, SULFURIC ASID. FROM 0.1 TO 1.0 OUNCE PER GALLON OF DEXTROSE AND FROM 0.005 TO 0.015 OUNCE PER GALLON OF 1-ACETYL-2-THIOHYDANTOIN. 